1. Field oft he invention
This invention relates to the production of cutout masks used in a reproduction process. In particular, the present invention relates to a layer process in the production of cutout masks.
2. Description of the Prior Art
Cutout masks are commonly used to produce process films in the reproduction process. The cutout masks are produced from processing peel-off films. The peel-off films are transparent (light-transmitting) film substrates with a coating of colored (typically red) light-shielding films. The light-shielding films are cut in a pattern, and any film area (peel portion) closed by the pattern may be peeled off, exposing transparent film substrates.
Assuming that a reproduction process starts with a mechanical 156 showing FIGS. 150 overlaps with FIGS. 151 and that a back ground 158 surrounds FIGS. 150 and 151, in FIG. 1A, the entire process to process films is as follows: First, peel-off films are so cut that peel portions are outlined as indicated in FIG. 1B and FIG. 1C. The peel portions are then peeled off, resulting in a cutout mask 152 in FIG. 1B and another cutout mask 153 in FIG. 1C. Original films 154 and 155, bearing FIGS. 150 and 151 respectively, are attached onto both cutout masks 152 and 153 so that their transparent portions 152a and 153a are correspondingly covered as shown in FIG. 1D and FIG. 1E. The cutout mask 152 is further attached onto a process film (not shown), and then an exposure step is taken. The process film is exposed through the FIG. 150, thereby in accordance with its location and patterns, wherein the location and patterns fall in the transparent portion 152a. The cutout mask 152 shown in FIG. 1D is then replaced with another cutout mask 153 shown in FIG. 1E. The process film is again exposed through the FIG. 151, thereby in accordance with its locations and patterns, wherein the location and patterns fall within the transparent portion 153a. As a result, the process film now bears both FIGS. 150 and 151 as shown in FIG. 1A.
Further to the above description, more detail description is given below on how both cutout masks 152 and 153 (see FIG. 1B and FIG. 1C) are produced from the mechanical 156 shown in FIG. 1A. Used in the cutout mask production process are a digitizer 20 (See FIG. 5A), a computer 21, a monitor 22, a keyboard 23 (See FIG. 5B) and a cutting plotter 26 (see FIG. 5C).
FIG. 2A shows a first prior art example of the cutout mask production. Presented on the screen of the monitor 22 (see FIG. 5B) are two frame drawings of the FIGS. 150 and 151 shown in FIG. 1A within them as shown in FIG. 2A(1). One frame drawing overlaps with the other frame drawing, forming a overlapping portion 80. Note that the two frame drawings are drawn, based on the graphic data derived from the digitizer 20 (see FIG. 5A). Similarly, the frame drawing of the entire mechanical 156 is presented on the screen.
Next step is to cut a set of the predetermined number of peel-off films according to the graphic data which are graphically presented on the monitor screen. In this case, a set of three peel-off films as shown in (2), (3) and (4) of FIG. 2A are prepared and cut in the same pattern. The cutting plotter 26 performs the cutting step according to a signal from the computer 21. Referring to FIG. 5C, a cutting head 26C of the cutting plotter 26 cuts a peel-off film 30 set up on the cutting plotter 26.
The cut peel-off films, (2), (3) and (4), are then transferred to a factory peeling crew. The crew peel off the peel-off films, completing the cutout mask production step. It should be noted that each of peel-off films, (2), (3) and (4), has peel portions of T1, T2, T3, T4 and T5, all in common (see the peel-off film in FIG. 2A(1)). The crew have to determine what combination of peel portions to peel, referring to how frame drawings are overlapped in the mechanical 156 shown in FIG. 1A. In FIG. 2A (5), (6), and (7), hatching represents light-shielding portions and the blanks represent transparent (peel) portions. The cutout mask (5) is obtained by peeling the peel portion T5 off the peel-off film (2), and the cutout mask (6) is obtained by peeling the peel portions T3 and T4 off the peel-off film (3). The cutout mask (7) is obtained by peeling the peel portion T2 off the peel-off film (4). The cutout mask (7) is a film used to expose the process film for the background portion 158 (see FIG. 1) surrounding the FIGS. 150 and 151 in the mechanical 156.
Next step is to perform a choke and spread process to the cutout masks (5) and (7). The choke and spread process is to avoid in prints blanked borders which are due to a misaligned setup, likely to happen in the reproduction process. For example, when a misalignment takes place between the cutout masks (5) and (7) in FIG. 2A, a blank line may be created on the border 159 where the FIG. 150 and the FIG. 151 meet as in FIG. 1A. As choke and spread offset means for avoiding such a blank line, a transparent portion 82 on the cutout mask (5) is slightly enlarged so that its edge spreads over a transparent portion 83 on the cutout mask (6), when both cutout masks are set up. In the same manner as above, the choke and spread process is performed to the cutout mask (7) so that no blanked borders take place where the background portion 158 meets either the FIG. 150 or the FIG. 151. The width of enlarging the transparent portions is normally 50 .mu.m to 75 .mu.m. Such a degree of spread width in figures is too small to be noticed; thus, the choke and spread process will never affect the sharpness of prints.
In this prior art example, the choke and spread process adopts a reversing technique as illustrated in FIG. 2B. A cutout mask 70, a diffusion film 72, and a process film 74 to be choke-and-spread processed are stacked in a sandwich construction. The diffusion film 72 is of a film type that allows light to diffusively transmit. To perform the choke and spread process, light is directed to a transparent portion 70a of the cutout mask 70 in the direction of an arrow mark 100. The process film 74 is exposed to light which has passed the transparent portion 70a and then the diffusion film 72 in a diffusive manner. As a result, the choke and spread process has completed to the process film 74, with its transparent portion 74a being slightly larger than the transparent portion 70a of the cutout mask 70.
Referring to FIG. 3A, a second prior art example of producing the cutout masks 152 and 153 (see FIG. 1B and FIG. 1C) is described below. In a similar manner as in the first prior art, a display (8) is presented on the screen of the monitor 22 by means of the digitizer 20 (see FIG. 5A and FIG. 5B). The display (8) is made up of a first frame drawing 91, a second frame drawing 92, and a third frame drawing 93. The first frame drawing 91 shows the outline of the entire mechanical 156 in FIG. 1A. The second frame drawing 92 shows a frame of the FIG. 150, and the third frame drawing 93 shows another frame of the FIG. 151. The second frame drawing 92 overlaps with the third frame drawing 93, making the overlapping portion 80.
In this prior art example, the frame drawings are grouped to produce a required number of mask layers on the screen of the monitor 22. The choke and spread process is also performed along with this grouping step. More specifically, the frame drawings are once stored, and then the choke and spread process is performed by enlarging the portion T5 derived from excluding the overlapping portion 80 from the third frame drawing 93 on the screen of the monitor 22 as shown in FIG. 3A(9) and FIG. 3A(12). FIG. 3B is a detail drawing of display (9). A first step of the choke and spread process is to contract the second frame drawing 92. The contracted drawing is here designated 92X. A point P6 is one of the frame drawing 92X's corners which falls in the overlapping portion. A point P1 is the intersecting point where the frame drawing 92X meets the top side of the third frame drawing 93. A point P2 is the intersecting point where the frame drawing 92X meets the right side of the third frame drawing 93. A next step is to select a spread drawing for the choke and spread process. The spread drawing (see FIG. 3A(12)) here is a closed area formed by connecting the corner P6, points P1, P2 and three corners P3, P4 and P5, of the third frame drawing 93. After that, the first frame drawing 91, the second frame drawing 92, and the contracted frame drawing 92X are then all erased.
Next, the layer process starts with the display (10) in FIG. 3A. Both the first frame drawing 91 and the third frame drawing 93 should be first erased. This step is to produce the mask layer bearing the second frame drawing 92 only as illustrated in display (13).
Furthermore, another mask layer as in the display (14) is produced which corresponds to the background portion 158 in FIG. 1A. The choke and spread process of this mask is performed by combining the first frame drawing 91 and the second frame drawing 92 to form a frame drawing 94 as in display (11) of FIG. 3A, and then by contracting the frame drawing 94. A display (14) shows the contracted frame drawing 90N, which is already choke-and-spread processed. A digitizer input device 20M on the digitizer 20 is used to instruct graphic commands, like selecting, enlarging, or contracting drawings.
As mentioned above, three mask layers, shown in the display (12), the display (13) and the display (14), have been produced, through the mask grouping procedure based on the graphic data in the display (8), in FIG. 3A. These mask layer data are used to cut peel-off films, leading to the peel-off films (15), (16) and (17) in FIG. 3A. The peel-off films are then handed over to peeling crew who then peel off the peel portion T6, T7 or T8. The cutout masks (18), (19) and (20) have now been produced.
The prior art cutout mask production techniques, however, involve the following problems. In the first prior art example, the cutting patterns on the peel-off films (2), (3) and (4), are identical as shown in FIG. 2A. Thus, peeling crew have to determine what peel portions to peel and group mask layers for each final cutout mask. In case of FIG. 1F where a mechanical is composed of many overlapped figures, many combinations of figures are expected in a single mask layer. It is rather difficult to make a judgement in combining figures keeping the number of masks to a minimum. Peeling crew thus need long and experienced skill. Since peeling crew unavoidably have their own characteristics or preference in peeling work, they fail to produce cutout masks up to an established standard, and thus the integration and standardization of the peeling work cannot be reached. Also, when a cutout mask needs modifying after its full process of production, for example, the modification work should be done by the same crew who peeled off that cutout mask rather than some other crew. Furthermore, the first prior art example employs the reversing technique for the choke and spread process as illustrated in FIG. 2B. This technique allows the spread width to vary dependent on the exposure time in use. To reach the spread width, data on exposure or other related controls should be strictly managed. Such otherwise unnecessary management items are problematic from the viewpoint of quality assurance of cutout masks.
In the second prior art example, layering is performed by grouping drawings on the screen of the monitor 22. Each peel-off film has different cutting pattern for desired mask. Unlike the first prior art example, there is no need for peeling crew to determine which portions to peel off. Since the choke and spread process is performed along with the layer process on the screen, no reversing step as in the first example is required. This allows spread width to be set in a secure manner.
On the other hand, the second example has following disadvantages. When the third frame drawing 93 is in the choke and spread process as in FIG. 3B, the second frame drawing 92 needs contracting first. This means that a drawing itself which does not need choke and spread process should be graphically manipulated taking into consideration its spatial relationship with other drawings. Such an additional manipulation affects low productivity. In case of FIG. 1F where a mechanical is composed of many overlapped figures, spatial relationships among them are very complex. Even more time is needed. In the second example, the layer process is performed on the screen of the monitor. Therefore, when spatial relationships in figures are complex, it is not easy to determine, referring to displays on screen, which combination of figures gives which required mask. The layering task is thus a time consuming one. Since the layer process is associated with the choke and spread process, the overall task is even more complex.